1. Field of the Invention
The invention relates to a method of initiating a conference call and to a respective arrangement in a telecommunication system.
2. Description of the Related Art
The most common service provided by radio telecommunication systems has long been a point-to-point telephone call. The systems have provided only mobility as a new feature compared to fixed communication systems. Nowadays, modern radio telecommunication systems offer users a wide variety of services in addition to a normal phone call.
Modern telecommunication systems may offer the users a possibility to communicate in the telecommunications system for example with an Internet Protocol Multimedia Subsystem (IMS) as defined by the 3GPP (3rd Generation Partnership Project). The IMS provides the radio system with multimedia services which usually, although not necessarily, are Internet-based services employing a packet protocol. In an implementation, the IMS maintains a list of the services it offers and their preferred access types, which may comprise radio access or network access types, or both. To exchange messages with the IMS, user equipment may in some systems use what is known as a Session Initiation Protocol (SIP), which is used in third generation systems for controlling sessions, especially multimedia sessions, in the packet network.
A conference call is a service where a call is established between three or more participants. Each participant in the conference call is able to monitor the transmissions of all other participants and to make their own transmissions that can be received by all other participants. The transmission may be audio, such as in an ordinary call, or it may also comprise other media, such as video. All participants need not receive the same media. Thus, some participants may have a video connection and some an audio connection. The number of participants in an on-going conference call may vary.
The participating group may be a preselected group of users in the system. For example, a user may have user equipment with an address book comprising individual phone addresses and groups of several participants. Thus, with a single selection the user may initialize a group call with a predefined participant list.
Telecommunication systems supporting conference calls comprise one or more conference call servers, which manage conference calls, maintain call related signalling and are responsible for sending media streams to each participant. The actual implementation of a conference server may be realized with one or more physical servers.
In a telecommunication system, each party capable of communication has an address which identifies the party and with which the party can be contacted. In the SIP terminology the address is called a Uniform Resource Identifier (URI) or a SIP URI. It may, for example, have a form similar to an email address, or it may be a phone number. When a conference call is established in prior art systems, the party initiating the call must have certain information available before it can send a conference call set up message to the network. The user equipment must either know beforehand an address of a conference call server, or the user must dial in the address of that server manually. SIP also offers a user the possibility to create a conference by directly making use of the conference URI, where this URI has to be reserved and known by the network beforehand. A further option in a system utilizing SIP is that the user equipment has a conference-factory URI preconfigured in memory. In a system which utilizes SIP, the conference-factory URI is an address which responds to a call by creating a conference call. However, when no above-mentioned information is available, user equipment is unable to start a conference call.